(I knew that would wake people up… By the way, I just noticed and removed the restrictions on comments. Now anyone can comment on my posts, though I will restrict it again if people start spamming the blog.)
In the buildup to the war, the "military experts" were united in their criticism of Rumsfeld for supposedly deploying too few soldiers to the Iraqi front. Our forces were doomed, said the naysayers, because less than 150,000 of them were in theater, and not 400,000 or more as many wanted. Such a small force would be unable to control the country, and ananrchy would result.
Their worst fears seemed justified by the outbreak of looting in Baghdad, and later by the mass movement of terrorists across the border. But the looting could have easily been stopped had the local commander not been a slack-jawed overspecialized trees-before-the-forest type and appreciated how important civil order was in Iraq, and imposed martial law with summary executions of looters. And even a much larger force would have found it difficult indeed to police Iraq's huge, arbitrary border, though they would have had at least some additional impact.
More serious was the growth of no-go enclaves like Fallujah and (previously) Samarra. Here it is entirely possible that more troops would have allowed the commanders to deal with these cities sooner. That said, if 20,000 troops would have made a difference, 200,000 troops would have been overkill.
But what is lost in the debate is that any additional mobilization of forces on the Iraqi frontier would have posponed the beginning of the war by months at least. We know now that we are racing against the Iranians to see if we can turn over Iraq to the ING and free up our own forces before they build nukes; any delay would have been deadly. (On that note, we should fire or shoot the State Department idiots who opposed de-Ba'athification and the rebuilding of the ING. They lost us at least three crucial months.)
As well, a larger war effort would have been much more expensive. In the election, it would have made a huge difference if the war had cost $300 billion and not $100 billion so far (for example). It would have also made our stance against North Korea seem suspect and in danger of overreach.
Now, Iraqi units are coming online in great numbers. The terror groups are slowly being contained, civil order is largely restored, U.S. forces are freed up to go on the offensive, Samarra just kicked out the terrorists that had been based there, and things are looking favorable in general. Factoring in all the issues, I believe that Rumsfeld was justified in his decision.